In many industries, manufacturers of metal components have changed to structural adhesives to replace conventional fastening techniques such as rivets, bolts, and welding. Adhesives in theory offer many attractive properties that include improved product performance, aesthetics, reduced overall assembly time, and lower production costs. Additionally, adhesives preclude much of the stress point concentration, corrosion, and component damage often seen with rivets, bolts, welding, and other traditional fastening methodologies.
While conventional structural adhesives have made considerable progress in being able to bond a variety of substrates such as aluminum, cold-rolled steel, and carbon steel, conventional adhesives to cover a loss of strength over time on galvanized steel substrates. As a result of conventional structural adhesives failure to retain strength on galvanized substrates, various industries reliant on galvanized materials have retained traditional joinders such as welding and mechanical fasteners while suffering all the known limitations of these traditional processes.
Adhesive joinder of metal components has met with limited acceptance in various industries due to poor adhesion strength at elevated temperatures of 50° C., as well as low impact and yield strengths at −40° C. Additionally, conventional metal substrate joining adhesives tend to have inadequate shelf lives of six months or less at 20° C. Still further limitations of existing structural adhesives include low terminal lap shear strength and a slow build in handling strength that results in long fixture times that are contrary to efficient manufacturing throughput.
Thus, there exists a need for a structural adhesive formulation with improved adhesion at elevated temperature while offering a longer shelf life and superior thermal stability. There further exists a need for such an adhesive formulation offering a more rapid build of handling strength and a higher terminal lap shear strength even at reduced temperature so as to yield an adhesive able to bond a variety of structural substrates including galvanized metal.